1. Field of the Invention
This invention relates to a multi-path joint for joining various paths along which a variety of fluids flow, mixing the fluids together, and sending them downstream, and to a method for manufacturing the joint. Priority is claimed on Japanese Patent Application No. 2002-363611, filed Dec. 16, 2002, the content of which is incorporated herein by reference.
2. Description of the Related Art
There is a conventional joint for mixing together fluids by joining together a plurality of paths along which the fluids flow. The joint constitutes what is referred to in this invention as a multi-path joint, and has a function of connecting a great number of paths positioned upstream to at least one path positioned downstream.
One example of a general structure of this joint is explained below. Multiple lead-in ports for leading in multiple fluids are fitted to a housing, which forms the outer shape, and these lead-in ports are connected to a main path that runs through the inside of the housing. Since the multiple lead-in ports all lead to the main path, the fluids from each of the lead-in ports converge in the main path, and flow along it in a mixed state. The mixed fluids can then be led out simultaneously from at least one lead-out port, provided in an end face of the housing at the end of the main path.
This type of multi-path joint is used to discharge various fluids used in manufacturing semiconductors and the like as waste fluid, or in mixing fluids of various elements to supply one mixed fluid.
In this type of multi-path joint, since the lead-in ports on the inflow side for the multiple fluids are all joined via the main path to the lead-out ports on the outflow side for the converged fluids, when the flow of the fluid become slower, fluid amount becomes insufficient, and fluid pressure becomes lower as a result of the insufficient fluid amount, or the like, the mixed fluid in the main path may flow backwards to one of the lead-in ports.
When this happens, it can easily be envisaged that fluids of other elements in the upstream path connecting to the lead-in ports become mixed, and, in a worst case, there is a possibility that the mixed fluids will chemically react with each other, contaminating the atmosphere upstream of the main path.
Of course, since all the fluids are mixed in the main path, restrictions must be introduced to reduce reactions in the main path, such as using an alkaline or acidic solution, although reactions in the main path can be overlooked when the joint is provided with the aim of discharging all the fluids simultaneously. However, when fluids that flow independently along a path become mixed therein, neither the path nor the fluids can be used again.
Furthermore, when the joint is used for mixing fluids, chemical reactions between the mixed fluids are avoided by prior planning, and mixing in the main path presents no particular problem since that is the intention. However, when the mixed fluids flow backwards and become mixed into their respective paths, the elements of the fluids may change and cause considerable problems.
FIG. 6 shows a conventional method for preventing contamination of the atmosphere upstream caused by mixed fluid counterflow, wherein the paths are connected by reverse-stop valves 40, newly fitted to the lead-in ports 100a. In this method, adaptors 50 must be fitted between the respective reverse-stop valves 40 and the lead-in ports 100a. 
Furthermore, there is a conventional multi-path joint, which prevents the mixed fluid from flowing backwards toward the lead-in ports by providing a valve that seals the path between main path and the lead-in ports in the housing, the valve being controlled from the outside to open and seal the path leading to the lead-in ports (as shown in FIG. 2 of U.S. Pat. No. 5,035,262, for example).
In the structure disclosed in this multi-path joint, the motive force of a motor is converted via a gear to the operation of valves, which can be individually operated to open and seal each path individually. These valves are operated by externally controlling the power supplied to the motor.
In another structure, butterfly dampers are provided midway between each lead-in port and the main path, or at the end, the butterfly dampers being opened and closed by an external supply of air or the like.
The above-mentioned two structures for preventing mixed fluid in the main path from flowing backwards to the lead-in ports have at least one of the problems of being costly to install in the circuit, difficult to manufacture, expensive to manufacture, and incompatible for multiple path connection.
Firstly, the method of fitting the reverse-stop valves 40 to the lead-in ports 100a as shown in FIG. 6 has problems in that it requires a fitting operation for every single lead-in port 100a, and, in addition, greatly increases the size of the multi-path joint 100 after the reverse-stop valves 40 have been fitted. The former structure requires time prior to installation, and the latter structure may make it impossible to install in the fluid circuit due to space restrictions. Furthermore, the increased number of connecting portions makes leakage more likely, and requires additional check of these connecting portions to prevent leakage.
Secondly, since there are no particular limitation regarding the number of upstream paths that are connected by a multi-path joint, a plurality of multi-path joints having various numbers of lead-in ports must be kept in stock. Alternatively, when the multi-path joint is manufactured in response to a request for a multi-path joint having a stipulated number of lead-in ports, it may not be possible to meet the customer's deadline, losing the customer's trust.
The multi-path joint shown in FIG. 6 enables the housing to be divided for each of the lead-in ports 100a, but requires a pedestal 101 containing the main path in order to secure the divided blocks 102, 103, and 104 when they have been connected. As a result, various pedestals 101 must be manufactured in accordance with the required number of lead-in ports 100a. Therefore, although this structure enables the diameter of each lead-in port 100a to be easily altered, it cannot easily achieve a multi-path joint that can easily be compatible with various numbers of fluids.
In addition, in the above-mentioned structures for providing valves or butterfly dampers inside the paths and opening and sealing the paths from the outside by using a motor air and the like, there are problems in that the structure of the multi-path joint becomes complex, and the cost is considerably increased due to the number of components and the need to install a control circuit.